Enclosures for containing and supporting electrical and electronic components are designed to meet several important requirements. One requirement is to provide physical support and protection to electrical assemblies contained therein. Another requirement is to shield electromagnetic interference (EMI) so that it does not interfere with the operation of specific components. Yet another requirement is to provide a cooling air flow through the enclosure to in order to remove heat that is generated by operating components.
One exemplary enclosure comprises a rack mountable storage enclosure, sometimes referred to as an equipment cabinet, for supporting electronic and electrical insertable units or components. A typical rack mountable storage enclosure, designed for the high-availability market, is equipped with multiple fan modules in order to provide a redundant air flow cooling system that is highly reliable and unlikely to fail. Such storage enclosures are also provided with EMI shielding. The fan modules are mounted inside the storage enclosure, typically in the back, and are easily replaced when one module fails. The storage enclosure is typically designed with an air plenum that draws air through individual internal components via the air flow cooling system. The air flow cooling system is typically designed such that individual components are sufficiently cooled, even if one of the fan modules fails. Hence, the operating system contained within the enclosure may continue to run, even when one of the fan modules has failed to operate. Accordingly, such failed fan module is subsequently replaced without incurring a total loss of cooling capacity.
The housing of electrical components, such as computers and test equipment, within rack mountable storage enclosures has led to numerous techniques for shielding the internally housed electrical assemblies or components. It is desirable to prevent electromagnetic fields generated by these assemblies from propagating and interfering with other electrical equipment operating in the vicinity. For purposes of this disclosure, the term electromagnetic interference (EMI) is understood to refer to electromagnetic emission and radiation that includes both electromagnetic interference (EMI) and radio-frequency interference (RFI). Both of these types of interference generate electromagnetic fields that can interfere with the operation of adjacent electrical equipment. Storage cabinets designed to shield such interference are commonly known as EMI cabinets.
One prior art storage enclosure having an EMI barrier and cooling fan module is illustrated in FIG. 1. More particularly, an EMI storage enclosure 10 is shown in partial phantom lines to illustrate the manner in which a plurality of electrical/electronic components 12, 14 and 16 are EMI shielded and cooled therein. A single cooling fan module 18 is shown supported within an upper rear corner of enclosure 10. However, it is understood that some prior art constructions utilize a plurality of cooling fan modules 18 supported along a rear portion of enclosure 10. Additionally, enclosure 10 is constructed such that individual face panels 22 of components 12-16 are sealed with individual EMI gaskets (not shown) along a front peripheral edge portion extending about enclosure 10 so as to form a front panel 26.
Optionally, an EMI shielded door can be hingedly attached to one edge of front panel 26 and sealed with EMI gaskets there along to suppress EMI/RFI emissions during normal operation, and to permit access to components housed within enclosure 10. U.S. Pat. No. 5,049,701 to Vowles et al. teaches an EMI enclosure having a front door for carrying rail-supported components therein, and is herein incorporated by reference.
Where individual face panels 22 are used to form at least part of front panel 26, it is necessary to provide EMI shielded joints between the face panels 22 and leading edge of front panel 26. U.S. Pat. No. 5,294,748 to Schwenk et al., herein incorporated by reference, discloses the use of contact strips formed from an electrically well-conducting material interposed between panels, and extending along joints formed therebetween. Other EMI gasket constructions are known in the art. U.S. Pat. Nos. 5,483,423; 5,704,117; and 5,734,561 show additional techniques for imparting EMI shielding along a joint or connection, and are herein incorporated by reference.
As shown in FIG. 1, EMI storage enclosure 10 includes a framework (not shown) comprising a plurality of frame members onto which face panels 22, front panel 26, back panel 28, top panel 30, bottom panel 32, and side panels 34 and 36 are secured in a manner that suppresses EMI/RFI emissions. One technique for affixing such panels uses a strip of conductive finger-like springs to form a wiping electrical contact between the panels and framework. Other techniques are also well understood in the art including welding individual panels together, or to the framework. It is also understood that a plurality of horizontally extending rails are formed along inner-surfaces of panels 28,34 and 36 for supporting rack-mounted electrical/electronic components, such as components 12, 14 and 16.
Also shown in FIG. 1, a plurality of inlet apertures 20 are formed in front panel 26; namely, in individual face panels 22. Apertures 20 allow cooling air to be drawn from outside enclosure 10 and through front panel 26 via inlet air flow paths 38, 40 and 42. Apertures 20 can be round, elliptical or any suitable shape. More particularly, cooling fan module 18 contains a motor-driven fan that draws air through inlet apertures 20, within individual components 12-16, exiting components 12-16 via outlet air flow paths 44, 46 and 48, and into a common air plenum 26. Cooling fan module 18 then draws air from within plenum 24, via a cooling module flow path 50, and forces the drawn air out through back panel 28 of enclosure 10 via a common outlet flow path 52 provided by a plurality of relatively small sized exhaust apertures 56.
FIG. 2 illustrates the prior art storage enclosure 10 of FIG. 1 in vertical-sectional view taken lengthwise. A fan inlet port 58 is shown communicating with a relatively large air plenum 44 that is formed in an inner portion of enclosure 10, behind components 12-16. The flow of cooling air through enclosure 10, as moved by fan module 18, is clearly shown in FIG. 2. Cool air is drawn into enclosure 10, and into individual components 12-16 via inlet paths 38, 40 and 42. Apertures (not shown) are provided in the rear of each component 12-16 such that cooling air, now slightly heated, leaves components 12-16 via outlet paths 44, 46 and 48 and enters a common enclosure or air plenum 24. Cooling fan module 18 withdraws the slightly heated cooling air from plenum 24 through port 58 and ejects the air from enclosure 10 via the plurality of relatively small exhaust apertures 56 formed in back panel 28, adjacent cooling fan module 18.
Pursuant to the construction of enclosure 10 depicted in FIGS. 1 and 2, an electromagnetic interference (EMI) barrier 54 is provided by enclosure 10. Inlet apertures 20 and exhaust apertures 56 are dimensioned with a size that prevents escape of undesirable frequencies of electromagnetic interference (EMI) and radio-frequency interference (RFI) from enclosure 10. For example, smaller aperture sizes are needed to prevent escape of higher frequency components emanating from electromagnetic fields generated by operating components contained within enclosure 10. The escape of such high frequency components, or the escape of any electromagnetic/radio-frequency waves, can interfere with the operation of other electrical/electronic equipment that is adjacent to, but outside of, enclosure 10. Accordingly, it is well understood in the art to appropriately size and shape inlet apertures 20 and exhaust apertures 56 so as to prevent escape of undesirable EMI/RFI components.
However, there have been recent desires to minimize the size of rack mounted storage systems, or enclosures. More particularly, market pressures have caused manufacturers of storage enclosures to reduce the size of rack mounted storage systems. As a result, the surface area available on the rear face, or panel, of many storage enclosures has become smaller and smaller. Hence, the surface area available for exhausting cooling air from the enclosure has been significantly reduced, which means that cooling fan modules are required to more forcibly exhaust cooling air through a more limited number of exhaust apertures provided across a smaller surface area.
Additionally, there has been a change in how individual components are signal coupled together within a storage enclosure. In the past, components within a storage enclosure were coupled together using Small Computer System Interface (SCSI). Recently, Fibre channel technology, such as fiber optic cables and connectors, have been used to connect together components within a storage enclosure. However, Fibre channel technology generally generates electromagnetic interference (EMI) emissions at much higher frequencies than SCSI technology.
In order for a storage enclosure, such as enclosure 10 of FIG. 1, to contain these higher frequencies, the hole sizes for inlet apertures 20 and exhaust apertures 56 are required to be very small. However, reducing the size of apertures 20 and 56 can significantly restrict the ability of cooling fan module 18 to push exhausted cooling air through exhaust apertures 56, via outlet flow path 52. For most designs, front panel 26 contains sufficient surface area in order to increase the number of smaller-sized inlet apertures 20. However, the above-mentioned efforts to reduce the size of storage enclosures usually results in insufficient surface area being provided in back panel 28, along cooling fan module 18, in order to increase the number of smaller-sized exhaust apertures 56.
To make matters worse, the fans within cooling fan modules are required to blow, or push, cooling air through these relatively smaller-sized exhaust apertures, which proves to be much more difficult and inefficient than drawing cooling air through these smaller-sized exhaust apertures. As a result, recent attempts to reduce the hole size of exhaust apertures has generated a loss of margin, or inefficiency, in volumetric air flow which has reduced heat dissipation from storage enclosures.
Accordingly, there exists a need to provide an improved storage enclosure having an EMI/RFI barrier suitable to restrict propagation of higher-frequency emissions from within the storage enclosure to the exterior of the storage enclosure.
There exists a further need to provide a storage enclosure capable of shielding internal components from relatively low frequency emissions generated by a cooling fan module, while still enabling an efficient flow of cooling air through the storage enclosure.
There exists even a further needed to provide a technique for shielding, or separating, components within a storage enclosure such that EMI/RFI emissions from one component are prevented from interfering with a second component.